DESCRIPTION (Adopted from applicant's abstract): Angiotensin II (AII), an octapeptide that is a component of the renin-angiotensin system, is produced within the anterior pituitary gland of rats and humans, and appears to play a paracrine (rat) or autocrine (human) role in regulation of prolactin secretion. This research proposes to examine the effects of estrogen on rat lactotroph sensitivity to the paracrine mediator AII. Specifically, the hypothesis to be tested is that the pattern and levels of estrogen secretion (or replacement) influences anterior pituitary lactotroph sensitivity to AII-and LHRH-induced stimulation of prolactin secretion. Ovariectomized, prepubertal female rats will be injected with estrogen and progesterone to induce LH surges in a pattern that mimics estrous cyclicity. A second group of ovariectomized animals will receive no steroids, and a third group will not be ovariectomized. Anterior pituitary cells from these animals at six months of age will be exposed to physiological doses of AII and LHRH to determine the prolactin secretory response. Accumulation of inositol phosphates (IP), the second messenger which mediates the AII stimulation of lactotrophs, and AII receptor binding characteristics will also be investigated.